To get a custom field value outside of the loop you need to call global $wp_query
to get your post id.
global $wp_query;
$postid = $wp_query->post->ID;
$image = get_post_meta($postid, 'Thumbnail', true);
To get a custom field value outside of the loop you need to call global $wp_query
to get your post id.
global $wp_query;
$postid = $wp_query->post->ID;
$image = get_post_meta($postid, 'Thumbnail', true);